Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$71.90	9.393%	$78.6536	$78.65	$78.65	$78.70
Purchase #2	$53.93	6.335%	$57.3465	$57.35	$57.35	$57.30
Purchase #3	$170.80	5.844%	$180.7816	$180.78	$180.80	$180.80
Purchase #4	$147.84	13.188%	$167.3371	$167.34	$167.35	$167.30
Purchase #5	$97.85	11.648%	$109.2476	$109.25	$109.25	$109.20
Purchase #6	$189.55	8.332%	$205.3433	$205.34	$205.35	$205.30
Purchase #7	$56.54	5.863%	$59.8549	$59.85	$59.85	$59.90
7 purchase totals =	$788.41		$858.5646	$858.56	$858.60	$858.50